Maximum Volume Landscape Berm - Site Modeling

Good afternoon,

I'm trying to create a landscape berm where I will be able to use as much excess fill as I can while keeping the sideslope constant (4:1) and controlling the bottom of the berm with an outline and a set elevation (profile along the plan outline). I want to begin at the toe of slope and slope upwards at 4:1 until the slope intersects the other side of the berm, which is being defined the same way. 

From my attached image (sorry for the crude sketch), The white boundary is the toe of slope of the berm, which is set in both plan view and controlled via a profile for elevation. The elevation varies along the perimeter of the berm too. For an added bonus, I would like to create a minimum width flat are at the top of the berm, but that isn't 100% necessary at this time.

Any ideas on a way to be able to generate a surface with this criteria?

Thanks,
Ken

Geopak SS4 OpenRoads